Drill stack formation

ABSTRACT

The present invention provides a method of temporarily adhering a stack of sheets together to facilitate drilling a hole through the stack of sheets. The method includes using a temporary adhesive that prevents burring while drilling a hole through the stack.

BACKGROUND OF THE INVENTION

[0001] 1. Technical Field

[0002] The present invention relates to a method of temporarily adheringa stack of sheets together to facilitate drilling a hole through thestack of sheets.

[0003] 2. Related Art

[0004] A stack of sheets may be adhered together around a periphery ofeach sheet using an adhesive such as a glass cloth impregnated withepoxy. Hole burring occurs as a drill passes through the stack.Additionally, each sheet separates from an adjacent sheet as the drillpasses between the sheets. This results in the whole stack of sheetsexpanding. An alternate method includes the permanent application ofcured epoxy over the entire surface of each sheet in the stack. Thethickness of the epoxy between each sheet results in excessive thicknessof the overall stack as well as composites which will contain theseparated sheets when they are processed into composites. A method ofdrilling a stack of sheets that overcomes these problems plus others isdesired.

SUMMARY OF THE INVENTION

[0005] A first general aspect of the present invention provides astructure comprising:

[0006] a stack comprising a plurality of sheets such that eachsuccessive sheet is coupled with a removable adhesive between eachsheet; and

[0007] an opening extending through the plurality of sheets within thestack.

[0008] A second general aspect of the present invention provides astructure comprising:

[0009] a plurality of stacks wherein each successive stack is coupledwith a removable adhesive to an intermediate layer between each stackwherein each intermediate layer prevents burr formation; and

[0010] wherein each stack comprises a plurality of sheets such that eachsuccessive sheet is coupled with a removable adhesive between eachsheet.

[0011] A third general aspect of the present invention provides a methodcomprising:

[0012] forming a stack by stacking a plurality of sheets;

[0013] applying an adhesive between each successive sheet;

[0014] applying a vacuum to the plurality of sheets;

[0015] heating the plurality of sheets to melt the solid adhesive;

[0016] applying a first pressure to the sheets;

[0017] cooling the plurality of sheets; and

[0018] forming an opening through the plurality of sheets; and

[0019] separating the sheets.

[0020] A forth general aspect of the present invention provides a methodcomprising:

[0021] forming a stack by stacking a plurality of sheets;

[0022] applying a thin layer of water between each successive sheet;

[0023] applying a pressure to the sheets; and

[0024] forming an opening through the plurality of sheets.

BRIEF DESCRIPTION OF THE DRAWINGS

[0025] For an understanding of the present invention, reference shouldbe made to the following detailed description taken in connection withthe accompanying drawings wherein:

[0026]FIG. 1 illustrates a first embodiment of the present inventionincluding a side view of a laminated structure including a stackcomprising a plurality of sheets including a removable adhesive betweeneach sheet;

[0027]FIG. 2 illustrates a second embodiment of the present inventionincluding a side view of a laminated structure including a plurality ofstacks including a plurality of layers separating each stack;

[0028]FIG. 3 illustrates a third embodiment of the present inventionincluding an exploded side view of another embodiment of a laminatedstructure including a plurality of blotter sheets and a plurality platesadded to a stack;

[0029]FIG. 4 illustrates the laminated structure of FIG. 3 positionedwithin a press apparatus for forming a rigid stack;

[0030]FIG. 5 illustrates the rigid stack of FIG. 4 with a burr free holedrilled through each sheet of the stack;

[0031]FIG. 6 illustrates a plan view of a hole within a sheet of thestack; and

[0032]FIG. 7 illustrates a flow chart of a method for producing a burrfree hole in each sheet of the stack.

DETAILED DESCRIPTION OF THE INVENTION

[0033]FIG. 1 illustrates a schematic view of a laminated structure 10including a stack 12 in accordance with a first embodiment. The stack 12includes a plurality of sheets 14A-14L. A removable adhesive 16A-16K isapplied between each sheet 14A-14L, respectively. The sheets 14A-14L maycomprise any suitable material (e.g., copper, invar,copper-invar-copper, etc.). Invar is an iron-nickel alloy. The removableadhesive 16A-16K may comprise any suitable material (e.g., fructose,sucrose, water soluble polymers, water, etc.). The material may compriseany suitable form (e.g., powered fructose, a liquid, a liquid solution,etc.).

[0034]FIG. 2 illustrates a laminated structure 10A including a stack 12Ain accordance with a second embodiment. The stack 12A includes aplurality of stacks 12C, 12D, 12E, and 12F interspersed with a pluralityof layers 18A-18E. Each stack 12C, 12D, 12E and 12F includes a pluralityof sheets 14 with removable adhesive placed between each sheet 14. Also,the removable adhesive 16 is placed between each layer 18A-18E and eachadjacent sheet 14. Each layer 18B and 18C prevents chip build up withindrill bit flutes 21 by providing an interruption in the sheet 14 beingdrilled. Each layer 18A-18E comprises any suitable soft material (e.g.,impregnated and laminated epoxy/glass, phenolic/paper laminate,aluminum, etc.). The formation chips are broken off each time the drillbit 20 passes from one material to a dissimilar material. For example,if each sheet 14 is copper, and each layer 18A-18E is (aluminum orpaper/phenolic), then any tendency for chip build up would beinterrupted each time the drill bit 20 passes from copper to (aluminumor paper/phenolic), or from (aluminum or paper/phenolic) to copper.Additionally, the first layer 18A keeps the drill bit from wandering asit enters the stack 12A of the laminated structure 10A. A soft material,such as aluminum, assists the drill bit 20 in starting a hole 102 at adesired location without wandering about a top surface 22 of the layer18A.

[0035]FIG. 3 illustrates a laminated structure 10B including a stack 12Bin accordance with a third embodiment. The stack 12B includes aplurality of sheets 14. The removable adhesive 16 is applied betweeneach sheet 14. The stack 12B includes a first surface 24 and a secondsurface 26. A first surface 28A of a first layer 18F is coupled with theremovable adhesive 16 to the first surface 24 of the stack 12B. A firstsurface 30A of a second layer 18G is coupled with the removable adhesive16 to the second surface 26 of the stack 12B. A first surface 32A of afirst foil 34A contacts a second surface 28B of the first layer 18F. Afirst surface 36A of a second foil 34B contacts a second surface 30B ofthe second layer 18G.

[0036] A first surface 38A of a first plate 50A contacts a secondsurface 32B of the first foil 34A. A first surface 40A of a second plate50B contacts a second surface 36B of the second foil 34B. A firstsurface 42A of a third plate 50C contacts a second surface 38B of thefirst plate 50A. A first surface 44A of a fourth plate 50D contacts asecond surface 40B of the second plate 50B. The plates 50A-50D mayinclude any suitable material, such as stainless steel.

[0037] The laminated structure 10B includes a first blotter pad 60A anda second blotter pad 60B. The first blotter pad 60A includes at leastone blotter sheet 62, and the second blotter pad 60B includes at leastone blotter sheet 62. The blotter sheets 62 may include any suitablecompressible material, such as paper. The blotter pads 60A and 60Babsorb any misalignment between a pair of pressure surfaces 90A and 90B(FIG. 4) and the stack 12B, so that a uniform pressure is applied to thestack 12B.

[0038] A first surface 64A of the first blotter pad 60A contacts asecond surface 42B of the third plate 50C. A first surface 66A of thesecond blotter pad 60B contacts a second surface 44B of the fourth plateSOD. A second surface 64B of the first blotter pad 60A contacts a firstsurface 66A of a fifth plate 50E. A second surface 66B of the secondblotter pad 60B contacts a first surface 68A of a sixth Plate 50F. Theplates 50E and 50F may include any suitable material, such as stainlesssteel.

[0039]FIG. 4 illustrates the laminated structure 10B of FIG. 3positioned within a press apparatus 92. The press apparatus 92 includesa first pressure head 94A, a second pressure head 94B, a vacuum source96, and a heat source 98. The first pressure head 94A and the secondpressure head 94B provide a compressive force 100 to the laminatedstructure 10B. A second surface 66B of the fifth plate 50E contacts thepressure surface 90A of the first pressure head 94A. A second surface68B of the sixth plate 50F contacts the pressure surface 90B of thesecond pressure head 94B.

[0040]FIG. 7 illustrates a flow chart of a method for producing a burrfree hole 102 in each sheet 14 of the stack 12B (FIGS. 5 and 6). Step104 includes stacking a plurality of sheets 14 to form the stack 12B.Step 106 includes applying a removable adhesive 16 between eachsuccessive sheet 14 in the stack 12B. Step 108 includes applying theremovable adhesive 16 between the first layer 18F and the first surface24 of the stack 12B. As mentioned above, the removable adhesive 16 maycomprise any suitable material (e.g., fructose, sucrose, water solublepolymers, water, water solutions, etc.). The following example describesusing the removable adhesive 16 in the form of solid powered fructose.Step 110 includes applying the removable adhesive 16 between the secondlayer 18G and the second surface 26 of the stack 12B. Step 111 includesforming the laminated structure 10B by applying the foil sheets 34A, 34Bthe 50A-50F, and the blotter pads 60A and 60B to the stack 12B, asillustrated in FIG. 7. Step 112 includes applying a vacuum to thelaminated structure 10B using the vacuum source 96. Step 114 includesheating the laminated structure 10B to melt the removable adhesive 16.

[0041] Step 116 includes applying the compressive force 100 to thelaminated structure 10B. For fructose, the heat source 98 provides atemperature of about 50° C. to 200° C. and a first compressive force 100applied to the laminated structure 10B creates a pressure of about 25 to75 psig. After about 10 to 20 minutes, the fructose particles start tosoften, and the pressure is increased to about 200 to 400 psig. Theincrease in pressure is delayed to ensure that every fructose particlehas been softened to prevent denting of the sheets 14. The pressure andtemperature are held for about 5 to 15 minutes and then shut off and thelaminated structure 10B is cooled while maintaining pressure. When thestack is cool, the pressure is removed and the laminated structure 10Bis removed from the press apparatus 92.

[0042] In step 118, the laminated structure 10B is cooled to an ambienttemperature. In step 119, the foil sheets 34A, 34B, the blotter pads60A, 60B, and the plates 50A-50F are removed from the laminatedstructure, and the stack 12B and the attached layers 18F and 18G areremoved from the press apparatus 92. In step 120, a drill bit 20 drillsthe hole 102 through the stack 12B and the layers 18F and 18G, asillustrated in FIG. 5. In step 122, the stack 12B and the layers 18F and18G are dipped into a liquid solution 132 to dissolve the fructose. Forfructose, the liquid solution 132 may include an ethylene glycol/watermixture. In step 124 the removable adhesive is heated in the liquidsolution 132 temperature of about 130° C. to about 150° C. for about 5minutes to melt the removable adhesive 16. In step 126, the sheets 14are separated from each other using any su table device, such astweezers, clamping devices, etc. In step 128, each sheet 14 is rinsedwith any suitable liquid, such as, distilled water and/or a milddetergent solution. In step 130 each sheet 14 is dried using a gas, suchas hot dry air. Alternatively, the sheets 14 may be separated by placingthe stack 12B in a steam autoclave 134. In the steam autoclave 134,pressurized steam is driven between each sheet 14. The sheets 14 arethen separated, rinsed in water and dried. FIG. 6 illustrates a planview of the sheet 14 having formed a burr free hole 102.

[0043] While embodiments of the present invention have been describedherein for purposes of illustration, many modifications and changes willbecome apparent to those skilled in the art. For example, the removableadhesive 16A-16K may comprise a thin layer of water. The surface tensionof the thin layer of water between each sheet 14A-14L of the laminatedstructure 10A holds the laminated structure 10A together while the hole102 is drilled. Each sheet 14A-14L is peeled off the laminated structure10A and rinsed in additional water to remove any material particles.Then, each sheet 14A-14L is dried. Accordingly, the appended claims areintended to encompass all such modifications and changes as fall withinthe true spirit and scope of this invention.

We claim:
 1. A structure comprising: a stack comprising a plurality ofsheets such that each successive sheet is coupled with a removableadhesive between each sheet; and an opening extending through theplurality of sheets within the stack.
 2. The structure of claim 1,wherein the sheets comprise a material selected from the groupconsisting of copper, invar, copper-invar-copper, aluminum, andmolybdenum.
 3. The structure of claim 1, wherein the removable adhesivecomprises a material selected from the group consisting of fructose,sucrose, water soluble polymers, water, and water solutions.
 4. Thestructure of claim 1, further including: a first surface of a firstlayer coupled with the removable adhesive to a first surface of thestack wherein the first layer prevents burr formation; a first surfaceof a second layer coupled with the removable adhesive to a secondsurface of the stack wherein the second layer prevents burr formation;and wherein the opening further extends through the first and secondlayer.
 5. The structure of claim 4, further including: a first surfaceof a first foil contacting a second surface of the first layer; and afirst surface of a second foil contacting a second surface of the secondlayer.
 6. The structure of claim 5, further including: a first surfaceof a first plate contacting a second surface of the first foil; and afirst surface of a second plate contacting a second surface of thesecond foil.
 7. The structure of claim 6, further including: a firstsurface of a third plate contacting a second surface of the first plate;and a first surface of the fourth plate contacting a second surface ofthe second plate.
 8. The structure of claim 7, further including: afirst blotter pad comprising at least one blotter sheet; a first surfaceof the first blotter pad contacting a second surface of the third plate;a second blotter pad comprising at least one blotter sheet; and a firstsurface of the second blotter pad contacting a second surface of thefourth plate.
 9. The structure of claim 8, further including: a firstsurface of a fifth plate contacting a second surface of the firstblotter pad; and a first surface of a sixth plate contacting a secondsurface of the second blotter pad.
 10. The structure of claim 5, whereinthe first and second layer comprises a material selected from the groupconsisting of impregnated and laminated epoxy/glass, phenolic/paperlaminate, and aluminum.
 11. The structure of claim 6, wherein the firstand second foil comprises copper.
 12. The structure of claim 8 whereinthe first and second blotter sheet comprises paper.
 13. The structure ofclaim 9, wherein the fifth and sixth plate comprises stainless steel.14. A structure comprising: a plurality of stacks wherein eachsuccessive stack is coupled with a removable adhesive to an intermediatelayer between each stack wherein each intermediate layer prevents burrformation; and wherein each stack comprises a plurality of sheets suchthat each successive sheet is coupled with a removable adhesive betweeneach sheet.
 15. The structure of claim 14, wherein the sheets comprise amaterial selected from the group consisting of copper, invar,copper-invar-copper, aluminum, and molybdenum.
 16. The structure ofclaim 14, wherein the removable adhesive comprises a material selectedfrom the group consisting of fructose, sucrose, water soluble polymers,water, and water solutions.
 17. The structure of claim 14, wherein eachintermediate layer comprises a material selected from the groupconsisting of laminated and impregnated epoxy, aluminum, and copper. 18.A method comprising: forming a stack by stacking a plurality of sheets;applying an adhesive between each successive sheet; applying a vacuum tothe plurality of sheets; heating the plurality of sheets to melt thesolid adhesive; applying a first pressure to the sheets; cooling theplurality of sheets; and forming an opening through the plurality ofsheets.
 19. The method of claim 18, further including applying a secondpressure to the sheets, wherein the second pressure is greater than thefirst pressure.
 20. The method of claim 18, further including: dippingthe plurality of sheets into a liquid solution; heating the plurality ofsheets to a melting temperature of the adhesive; separating each sheetfrom the plurality of sheets; rinsing each sheet with water; and dryingeach sheet.
 21. The method of claim 18, wherein the adhesive isfructose.
 22. The method of claim 18, wherein the heat applied to theplurality of sheets is about 50° C. to 200° C.
 23. The method of claim19, wherein the first pressure is about 25 to 75 psig. and the secondpressure is about 200 to 400 psig.
 24. The method of claim 20, whereinthe liquid solution is an ethylene glycol/water mixture.
 25. The methodof claim 18, further including: applying a first layer to a firstsurface of the stack; applying a second layer to a second surface of thestack; and extending the opening through the first and second layer. 26.The method of claim 25, further including applying at least one platecontacting the first and second layer.
 27. The method of claim 26,further including applying at least one blotter pad to each layer. 28.The method of claim 27, further including applying at least one plate toeach blotter pad for providing a surface to apply pressure to the stack.29. The method of claim 28, wherein the at least one plate contactingthe first and second layer of the stack, the at least one blotter padapplied to each layer, and the at least one plate applied to at leastone blotter pad are removed from the stack before the opening throughthe plurality of sheets is formed.
 30. A method comprising: forming astack by stacking a plurality of sheets; applying a thin layer of waterbetween each successive sheet; applying a pressure to the sheets; andforming an opening through the plurality of sheets.
 31. The method ofclaim 30, further including: separating each sheet form the plurality ofsheets; rinsing each sheet with water for removing particles; and dryingeach sheet.